MELBOURNE — Most people think about the hard-shelled, pig-faced armadillo only when it darts across the highway and gets squashed under their car tire.

But the nine-banded armadillo, the only one of 20 species that lives in the United States, has quite a following.

Texans call them Hoover hogs. Mexicans hunt them and consider them a delicacy. South Americans liken them to chickens. And at Florida Institute of Technology in Melbourne, they are famous for catching leprosy.

''There is no other mammal except humans that can be used to study leprosy,'' said Eleanor Storrs, a biochemist at FIT who directs the world's largest collection of armadillos used for research.

''Leprosy cannot be grown in a test tube or in tissue cultures, so research would be very limited without them,'' Storrs said.

Leprosy is a bacteria that attacks the nerves and skin in humans, causing nodules, ulcers and scales to form on the skin, mainly on the hands and feet. It is a chronic disease and usually leads to the amputation of hands and feet as the nerves die.

Over the years, scientists injected the leprosy bacteria into mice, rabbits, squirrels, rats, guinea pigs and monkeys. Nothing happened.

But in the early 1970s Storrs discovered small leprous nodules on the limbs, underbody and ears of armadillos about a year after she inoculated them with the disease. In fact, leprosy thrives so well in their bodies that within two years, they die of it.

Under contracts with the World Health Organization and the National Institutes of Health, her colony provides about 300 armadillos a year to researchers around the world searching for a cure for leprosy.

Storrs, who collects the animals from the wild, inoculates another 150 armadillos with the disease, kills them and sends their infected tissue to the World Health Organization's tissue bank in London. Scientists use the tissue to make vaccine.

''The armadillo is one big test tube when it comes to leprosy,'' she said. ''But the armadillo is a very fascinating animal in other ways, too.''

While working on her doctorate degree in Texas in the 1960s, Storrs became fascinated with them because they are the only animal that produces genetically identical babies. They always have four babies; they are all the same sex and all look the same.

She still is trying to discover how some impregnated armadillos can delay birth for up to a year while in captivity. Several times, females have given birth even though they were kept in cages away from males for more than a year, she said. Their gestation period usually is about eight months.

Storrs thinks the animals may have an internal sperm bank.

Armadillos are not native to Florida. Almost all of them can be traced back to four animals brought from Texas in the 1920s by a Cocoa land developer for his zoo, she said.

The four armadillos, using one of their best skills, promptly escaped.

''It seems only fitting that we now have the world's largest armadillo colony right down the road from there,'' she said.

Neither the armadillo nor leprosy is native to America. The Spanish conquistadors brought leprosy in the 16th century. Armadillos migrated from Mexico in the 1850s and concentrated

mainly in Texas.

Storrs discovered the armadillo-leprosy link in 1971 while working with her husband at the U.S. Public Health Hospital for leprosy victims in Louisiana. She overheard researchers talking about how leprosy grows only in the cooler parts of the human body, such as the hands and feet.

It does not grow in the internal organs where the temperature stays 98.6 degrees Fahrenheit.

''I asked them if anybody had ever tried to inoculate an armadillo with leprosy because their body temperature is 90 to 92 degrees. They just laughed at me. I mean it must have sounded strange -- an armadillo.''

Later, she discovered armadillos with leprosy in the backwoods of Louisiana, and other tests on armadillo blood that had been frozen in the 1960s showed they had been exposed to the disease.

''There evidently was exposure to the disease way back before we ever thought about it. They also have found armadillos in Texas with leprosy in areas where there have been documented cases of leprosy in humans for a hundred years.

''One leprosy researcher in Texas studied five men with leprosy and as part of the study asked if they ever had contact with armadillos. All five said they had handled armadillos. That's not conclusive by any means but it sure is an interesting thought.''

Unlike armadillos, humans do not die of leprosy. They die of secondary diseases and infections that stem from it.

Today, leprosy poses a hazard only in Third World countries, where there are 15 million reported cases compared with 4,000 in the United States.

''Most people could never develop leprosy. That's a myth,'' Storrs added. ''In the countries where there is a lot of the disease, experts have found that only five percent are susceptible or ever develop it. Most people are immune to it.''